Can a Generator Be Hooked to the Power Grid at 180 Degrees Out of Phase?

[Evil Bunny]

What would happen if I hooked up a generator at my house (voltage and frequency identical) to the power grid and it was 180 degrees out of phase?

 

[Averagesupernova]

If you are lucky your generator would sputter a bit and 'phase itself' with the grid and continue to run or possibly trip a circuit breaker instead. Otherwise, some smoke may be involved.

 

[Evil Bunny]

So... the signals wouldn't cancel out? There would be zero volts at any given time during the cycle, right? Why would it try to "phase itself"?

 

[berkeman]

What would happen if I hooked up a generator at my house (voltage and frequency identical) to the power grid and it was 180 degrees out of phase?

So... the signals wouldn't cancel out? There would be zero volts at any given time during the cycle, right? Why would it try to "phase itself"?

It would look like a short circuit initially, with the grid's "output impedance" much lower than your generators'. So the generator would start to overcurrent in its output. If the phase were slightly off of 180 degrees, the large reverse current component would induce a short-term torque in the generator that would tend to synchronize the phase of your generator to the grid.

That's what happens in wind turbines in fields or water turbines in dams -- the objective of getting ready to connect the mechanical turbine/generator to the grid is to get the phase of the generator as close to the grid as possible, to minimize the mechanical stress on the turbine/generator when you close the switch to the grid...

 

[Evil Bunny]

I agree that the magnetic field forces would force the prime movers to synchronize in any situation other than a 180 degree phase difference, but I think that if they were exactly 180 degrees out of phase, we might have a different scenario...

 

[Averagesupernova]

I agree that the magnetic field forces would force the prime movers to synchronize in any situation other than a 180 degree phase difference, but I think that if they were exactly 180 degrees out of phase, we might have a different scenario...

I have heard of 180 degree mistakes being made at power plants and the generator being hooked to the grid goes through several cycles before phasing itself with the grid. I would think of it like trying to get a billiard ball to sit on top of a bowling ball. Sure you can position the billiard ball exactly on top of the bowling ball but its pretty unlikely it will sit there for very long. In the case of a small generator being hooked to the grid 180 degrees out of phase, what would happen is the small generator will be loaded heavily enough so that the engine slows slightly which changes the phase enough to sych up more easily. I doubt that a small generator will sit there and try to fight the situation 180 degrees out of phase. Of course, this is all assuming a fuse hasn't blown or breaker hasn't tripped.